Opposition lawmaker Son Chhay has asked Mines Minister Suy Sem to release detailed information about the export of silica sand – which was last month revealed to be exempt from a ban on sand exports – threatening “to impeach” the minister if he does not comply.

A letter dated Friday and sent to Sem through National Assembly President Heng Samrin requests that the Ministry of Mines and Energy release copies of the licences for companies mining and exporting silica sand in order to show transparency and avoid “confusion”.

It also requests a list of all sites approved for silica sand mining, environmental impact assessments and a list of countries that have imported the sand, as well as figures on the total amount of silica sand exported since November 2016 and how much it was sold for.

Chhay said by telephone that Sem had not “been fully cooperative in providing information” in the past and that his short replies last year at a committee hearing into the $700 million discrepancy in Singaporean and Cambodia customs data on sand trade would not be tolerated. “We would like to impeach him if he doesn’t respond,” Chhay said.

At least 30 members of parliament need to make a request for impeachment in order to push the matter to a National Assembly vote, and a two-thirds vote is required for it to pass, which would necessitate CPP cooperation.

Last year, the Mines Ministry temporarily suspended exports after the controversy erupted over the discrepancy between the $5 million of sand Cambodia recorded leaving to Singapore from 2007 to 2015 and the $752 million that Singapore recorded arriving from Cambodia.

The environmental group Mother Nature, which first revealed the discrepancy, last month claimed to show in a video that the exports were continuing. A ministry official at the time said the sand seen being loaded into a ship was “very likely” silica, which it said was not part of the ban.

The ministry released a statement saying it informed Cambodia’s shipping regulator of this on December 19 and officials in Taiwan confirmed vessels had brought silica there from Cambodia.

Mines Ministry spokesman Dith Tina said the ministry received Chhay’s letter yesterday.

“We always provide explanation to [the] public via journalists, to NGOs via open letter and forums and also to [the] National Assembly commission,” Tina said in an email, declining to respond to specific questions. “The accusation of [the] lawmaker . . . is just another provocation.”